How To Test The Fuel Pump -Dual Fuel Tanks (1993-1996 Ford F150, F250, F350)

TEST 2: Fuel Pump Pressure Test

We can easily test the FRONT and REAR tank fuel pumps with a fuel pressure test gauge.

If you don't have one, take a look at my recommendations in the section above or run down to your local auto parts store and buy or borrow one from them.

Here's the fuel pressure specification:

• If the engine starts: you should see 30 to 45 PSI.
• If the engine doesn't start: you should see 35 to 45 PSI.

NOTE: Whether your troubleshooting an 'engine does not start' problem or an engine performance problem (where the engine starts but runs bad), this section applies.

OK, these are the test steps:

1. 1

   Locate the Schrader valve on the fuel injector rail and place a shop towel underneath it.

2. 2

   Connect the fuel pressure test gauge to the Schrader valve.

3. 3

   Have your helper crank the engine while you while you check for fuel leaks around the Schrader valve/fuel pressure tester gauge connection.

4. 4

   Resolve any fuel leak (if present) at the connection before continuing to the next step.

5. 5

   Select the FRONT fuel tank.

6. 6

   Have your helper crank the engine while you observe the needle on the fuel pressure tester gauge.

7. 7

   The fuel pressure tester should give you a reading between 30 to 45 PSI.

8. 8

   Select the REAR fuel tank and repeat step 6 and step 7.

Let's examine your test results:

CASE 1: Both selected fuel tank fuel pumps registered the indicated fuel pressure. This is the correct test result and it lets you know that the front tank and rear tank fuel pumps are OK on your Ford F150 (F250 or F350).

This test result also lets you know that the fuel pump relay and fuel pump inertia switch are OK and doing their job.

If you're troubleshooting an 'engine does not start' problem, then you can conclude that the fuel pump (from either tank) is not behind the problem.

If you're troubleshooting an engine performance problem (where the engine starts but runs bad), then you can conclude that the fuel pump (from either tank) is not behind the problem.

CASE 2: One selected fuel tank fuel pump (but not both) registered 0 PSI. This test result lets you know that the selected fuel pump is not sending fuel to the fuel injectors and is causing the engine to not start.

This test result lets you know that the selected fuel pump (that registered 0 PSI) is bad and needs to be replaced.

CASE 3: One selected fuel tank fuel pump (but not both) registered a lower fuel pressure than the specification. This test result lets you know that the selected fuel pump is not supplying enough fuel to have the engine run optimally.

This is an indication that the selected fuel pump (that registered the lower than specified fuel pressure) is failing and needs to be replaced.

CASE 4: Both selected fuel tank fuel pumps indicated 0 PSI fuel pressure. This test result usually means that one of the following components is bad:

• The fuel pump relay.
• The fuel tank selector switch.
• The fuel pump inertia switch.

Although it's beyond the scope of this tutorial to test these 3 components, your next step is to test each one.

TEST 3: Using Starting Fluid

This is one of the very first tests I learned when I started out working on cars (back then most of them had carburetors -fuel injection was the new fangled thing).

This test is very effective in finding out if a lack of fuel (like from a bad fuel pump) is causing the engine to not start.

IMPORTANT: You have got to make sure that the ignition system is firing spark to the spark plugs before attempting the starting fluid test! This is important, since if there's no spark, this test is useless and, more importantly, indicates that the cause of the no-start condition is not due to a lack of fuel.

OK, these are the test steps:

1. 1

   Remove the intake air rubber duct from the throttle body. The end that connects to the air filter box can remain connected to it.

2. 2

   Manually open the throttle and spray starting fluid down the bore. Quickly reconnect the air duct to the throttle body (you don't have to tighten the hose clamp).

3. 3

   Have your helper crank the engine as you stand at a safe distance from the engine.

4. 4

   One of two things is gonna happen:
   
   1.) The engine will start, even if it's just momentarily or for a few seconds and then die or.
   
   2.) The engine will only crank but not start at all.

Let's take a look at what your test results mean:

CASE 1: The engine started, even momentarily. This lets you know that a lack of fuel is what is keeping the engine from starting.

Keep in mind that the starting fluid test is not an accurate way of testing the fuel pump (from either tank). I would still recommend testing the fuel pressure with a fuel pressure test gauge.

CASE 2: The engine did not start, not even momentarily. This lets you know that a lack of fuel is not the cause of your vehicle's no-start problem.

More 4.9L, 5.0L, and 5.8L Ford Tutorials

You can find more tutorials Ford F150, F250, and F350 in the following index:

• Ford 4.9L, 5.0L, 5.8L Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Test The Ford Ignition Control Module (Distributor Mounted).
• How To Test The Ford Ignition Control Module.
• Throttle Position Sensor (TPS) Test (Ford 5.0L, 5.8L).
• How To Test The Ford Mass Air Flow (MAF) Sensor.